Generally, contact lenses in wide use fall into three categories: (1) hard lenses formed from materials prepared by polymerization of acrylic esters, such as polymethyl methacrylate (PMMA), (2) rigid gas permeable (RGP) lenses formed from silicone acrylates and fluorosilicone methacrylates, and (3) gel, hydrogel or soft type lenses. The hard and rigid-type lenses, because they are characterized by low vapor diffusion and absorb only minor amounts of aqueous fluids, have a lower tendency to bind ingredients used in contact-lens care solutions. On the other hand, soft lenses have a greater tendency to bind active ingredients in contact-lens solutions and, therefore, it is especially challenging to develop solutions designed for the treatment of soft-type lenses, whether made from the more traditional copolymers of 2-hydroxyethylene methacrylate (HEMA) or from the newer silicon-containing hydrogel materials.
After wear, contact lenses must be disinfected to kill harmful microorganisms that may be present or grow on the lenses. Some of the most popular products for disinfecting lenses are multi-purpose solutions that can be used to clean, disinfect and wet contact lenses, followed by direct insertion (placement on the eye) without rinsing. Obviously, the ability to use a single solution for contact-lens care is an advantage. Such a solution, however, must be particularly gentle to the eye, since at least some of the solution will be on the lens when inserted and will come into contact with the eye.
U.S. Pat. No. 4,758,595 to Ogunbiyi et al. disclosed that a contact-lens solution containing a polyaminopropyl biguanide (PAPB), also known as polyhexamethylene biguanide (PHMB), has advantageous properties for a multi-purpose solution, especially in the presence of a borate buffer. These disinfecting and preservative solutions are especially noteworthy for their broad spectrum of bactericidal and fungicidal activity at low concentrations coupled with very low toxicity when used with soft-type contact lenses. Compositions containing PHMB and borate have been commercialized in various products including multi-purpose solutions, at relatively low levels of about 1 ppm or less, for use with soft contact lenses. U.S. Pat. No. 4,820,352 to Riedhammer discloses the use of poloxamine surfactants in general as cleaning agents in combination with biguanide disinfectants. U.S. Pat. Nos. 5,817,277; 5,593,637; and 5,422,073 to Mowrey-McKee et al. disclose a multi-purpose solution comprising a polyhexamethylene biguanide (PHMB) disinfectant in combination with the surfactants tyloxapol, poloxamine, or poloxamer for cleaning and disinfecting contact lenses.
A significant challenge to improving the cleaning efficacy of a multi-purpose solution is to simultaneously improve or maintain its disinfecting efficacy. The addition of more effective cleaning agents sometimes has the effect of reducing the efficacy of the disinfecting agent, in particular reducing the stability of the disinfecting agent over time. In particular, it is known that polymeric biguanides are not completely stable over time, hence requiring a limited shelf life when used at relatively low concentrations that are preferred for comfort reasons. Another challenge has been to develop a formula that is, on the one hand, maximally efficacious and, on the other hand, sufficiently gentle to be not only safe, but also comfortable for in-the-eye use.
One type of product that would require more efficacious cleaning and disinfection is a multi-purpose solution that would not require digital rubbing of the contact lens with the solution as part of its regimen of use. With conventional contact-lens cleaners or disinfectants, including multi-purpose solutions, lens wearers typically need to digitally or manually rub the contact lenses (typically between a finger and palm or between fingers) during treatment of the contact lenses. The necessity for the daily "rubbing" of contact lenses adds to the time and effort involved in the daily care of contact lenses. Many contact-lens wearers dislike having to perform such a regimen or consider it to be inconvenient. Some wearers may be negligent in the proper "rubbing" regimen, which may result in contact-lens discomfort and other problems. Sometimes rubbing, if performed too rigorously, which is particularly apt to occur with beginning lens wearers, may damage the lenses. This can be especially problematic when a replacement lens is not immediately available.
Contact lens solutions that qualify as a "Chemical Disinfecting Solution" do not require rubbing to meet biocidal performance criteria (for destroying representative bacteria and fungi) set by the U.S. Food and Drug Administration (FDA) under the Premarket Notification (510 k) Guidance Document For Contact Lens Care Products, May 1, 1997. In contrast, a contact-lens solution, referred to as a "Chemical Disinfecting System," not qualifying as a Chemical Disinfecting Solution, requires a rubbing regimen to pass biocidal performance criteria. Traditionally, multi-purpose solutions (used for disinfecting and wetting or for disinfecting, cleaning, and wetting) have qualified as a Chemical Disinfecting System, but not as a Chemical Disinfecting Solution.
Traditional contact-lens multi-purpose solutions may depend on a rubbing regimen, not only for efficacious disinfection, but also for efficacious cleaning. Thus, in order to develop a contact-lens care solution that would not require rubbing, both improved or stronger cleaning and disinfection may be needed, while at the same time maintaining the solution sufficiently gentle for in-the-eye use.
Thus, it would be desirable to obtain a multi-purpose contact-lens solution that would provide increased disinfecting efficacy, particularly over time. Further, it would be desirable to obtain improved cleaning efficacy while maintaining or increasing the biocidal efficacy of the product without adversely affecting the comfort or safety in terms of the level of toxicity to eye tissue. While still more challenging to develop, it would also be desirable to develop a multi-purpose solution that exhibits both efficacious cleaning and disinfection of a contact lens, without requiring a rubbing regimen, or at least not inherently or invariably requiring it for acceptable performance, which multi-purpose solution allows direct placement of the contact lens on the eye following soaking